Aldosterone regulation in primary aldosteronism: influence of salt balance, posture and ACTH

The response of aldosterone to manipulations of the renin-angiotensin and hypothalamic-pituitary-adrenal systems has been studied in thirteen patients with primary aldosteronism due to a single adenoma (ten patients) or bilateral hyperplasia (three patients). The aldosterone response to dietary sodium restriction was small and variable, although urinary aldosterone excretion increased in nine out of twelve studies. The response of patients with hyperplasia could not be distinguished from those with adenoma. All patients were unresponsive to salt loading. By contrast, plasma aldosterone fell in all patients after overnight dexamethasone (1 mg) and increased after brief (1 h) physiological ACTH stimulation. During prolonged erect posture, plasma aldosterone increased in the three patients with hyperplasia and decreased or remained unchanged in patients with ademona. Changes in plasma renin activity were similar in both groups. These studies show that patients with primary aldosteronism, while largely unresponsive to manipulations of sodium balance, retain sensitivity to small and acute changes in ACTH. The different behaviour of patients with hyperplasia to prolonged erect posture cannot be explained by insensitivity to ACTH, but could be due to a relative increase in sensitivity to angiotensin.